1. Filed of the Invention
This invention relates generally to the art of metal deformation, and is concerned primarily with the formation of helixes from thin walled metal tubes, particularly those clad with precious metals.
2. Description of the Prior Art
In the manufacture of tubular hoop-shaped earrings and other like jewelry products, elongated straight tubes are conventionally drawn from blanks consisting of a base metal such as brass with a surface layer of a precious metal such as 14 karat gold bonded thereto. Typically, the brass will be approximately 0.004 inches in thickness, and the gold surface layer will be 0.005-0.007 inches thick. The tubes are then manually bent or wrapped around cylindrical mandrels to form helixes. The thus formed helixes are next cut into individual hoops. The hoops are acid etched to remove the base metal, and are then assembled with other components to complete the finished articles.
Prior to being bent into helixes, the tubes are conventionally filled with sand and their ends are pinched shut. The sand is intended to avoid or at least minimize wrinkling and crimping during the manual bending operation. However, experience has indicated that even when the tubes are filled with sand, some wrinkling along the inside surfaces of the hoops is still experienced, thereby resulting in an unacceptably high reject rate. While somewhat beneficial in minimizing wrinkling, the sand becomes the source of other problems during subsequent manufacturing steps. More particularly, when subdividing the helixes into individual hoops, the sand has a deleterious effect on cutting equipment, in particular causing rapid wear and necessitating frequent changes of saw blades. The sand also presents cleaning problems. Failure to effect complete sand removal can adversely effect subsequent etching procedures.
The manual bending operation also results in some "spring back" of the helix convolutions. This in turn adversely affects product uniformity, and in extreme cases can be the cause of further rejects.
Finally, because of the difficulties encountered in manually bending tubes around cylindrical mandrels, this practice has been limited to round cross sectional configurations. Other tube configurations, e.g., ovals, rectangles, etc. have generally been avoided.
A general objective of the present invention is to provide an improved apparatus for forming thin walled metal tubes into helixes.
A more specific objective of the present invention is to provide an apparatus which is capable of bending thin walled tubes into helixes without first filling the tubes with sand, and without accompanying spring back.
Still another objective of the present invention is the provision of an apparatus capable of forming helixes from thin walled tubes of varying cross sections, including rounds, ovals and straight-sided configurations.